This invention relates to a device for shearing an opening in a rupture disk. In more detail the invention relates to a device for shearing an opening in a rupturable member which includes means for positively removing the sheared-out portion of the member from the opening. In still more detail the invention relates to an intermediate heat transport system (IHTS) for a liquid-metal-cooled nuclear reactor (LMFBR) incorporating a rupturable member, and means for cutting a large opening in the rupturable member and for positively removing the sheared-out portion of the rupturable member from the opening.
The heat developed in a LMFBR is removed therefrom by a Primary Heat Transport System (PHTS) and the heat thereof is transferred to an Intermediate Heat Transport System (IHTS) in an Intermediate Heat Exchanger (IHX). Sodium is normally used as coolant in both systems and the secondary sodium in the IHTS is employed to boil water and superheat the resulting steam.
It has been proposed that the IHTS of a LMFBR be provided with means for draining the sodium therefrom rapidly on command from a plant operator or from a sensor detecting a sodium-water accident within the system to limit the transport of corrosive liquid and solid sodium-water reaction products and so avoid damage to expensive, vulnerable pumps. It is necessary that the valves through which the sodium is drained must form a hermetic seal for the sodium which remains intact during normal and upset plant conditions while retaining the capability of being opened on command.
Present plans to accomplish this dumping are to drain simultaneously through multiple, relatively large lines connected in parallel from the IHTS loop to a dump tank. Plans are to include two normally closed valves in series in each drain line so that the total sodium inventory of the system can be maintained as consistent as possible over long periods. Such an arrangement would not be completely satisfactory in view of the long plant life (30 years) planned for LMFBR's. Over 30 years even the slight amount of leakage with the best current valve practice (2 cc/hr./in. seat diameter) may accumulate to a significant amount and also the high contact loadings between seat and disk of the tightly closed valves in high temperture sodium may result in self-welding of these mating parts jeopardizing the reliability of the system.
It has also been suggested that the foregoing problems might be satisfactorily answered by use of a mechanically actuated rupture disk which would be welded into position to positively seal the drain line. However, a conventional rupture disk such as those employed for pressure relief would not be satisfactory since a tear or small opening in the disk would dissipate the pressure but solid products from a sodium-water reaction might not pass through a tear or small opening. In addition, if parts of the rupture disk are free to move downstream, they may lodge somewhere in the drain line and cause solid reaction products to accumulate therein. Thus, it is essential that
1. the rupture disk must have an opening in it at least equal to that possible with a valve and
2. there must be no loose parts generated by the rupturing.